Virtual pre-embedding and electron microscopy.

<p>To obtain more information about the abundant diffuse neuropil labelling as observed with standard immunoperoxidase/DAB light microscopy, here we used the high sensitivity VirP labelling for light microscopy (A–C) and DAB-based immune-electron microscopy (D–G). With VirP, a clearly structured neuropil displaying numerous punctate profiles became evident in cerebral cortex (A) and hippocampus (B, C). The areas labelled by arrows are displayed at higher magnification in the insets in A–C. The labelled punctate profiles partly delineated dendritic profiles (asterisk in inset in B; arrowheads in inset in C), thus suggesting a synaptic localization of the antigens. With electron microscopy, ADC was localized to dendrites (D) and dendritic spines (E; compare unlabelled spines marked by asterisks), while Arg-like immunoreactivity was detected in presynaptic spine terminals (F). Postsynaptic densities of asymmetrical spine synapses are indicated by arrowheads. In neuronal cell bodies (G), the frequently displayed Arg-like punctate immunoreactivity was localized to numerous Golgi compartments including pre-Golgi buds at the endoplasmic reticulum (arrowhead in G). Rarely, immunoreactivity could also be attributed to ruptured mitochondria. Scale bars represent 20 µm in A–C; 5 µm in insets in A–C; 200 nm in D, E, inset in G; 100 nm in F; 500 nm in G.